Get out of the rut of researching Internet's gigantic genealogy databases. They are extremely worthwhile, but there is much more to explore on the Internet. I have discovered many great web sites for Illinois. They offer digital images.
The Illinois Digital Archives is worth checking. I recommend that you begin by clicking on the Collection Directory. This will give you an idea of what is there, then you can browse and search. There is also a help site if you have questions. Some of the collections include Illinois Veterans History Project, Illinois State Highway Maps, Illinois Historic Aerial Photographs and collections of various state historical societies and libraries.
Another great digital collection is the Illinois Historical Digitization Projects from the Northern Illinois University Libraries. Some of the projects include Illinois during various periods, such as the Civil War, 1861-1865, The Mexican-American War and Illinois Civil War Newspapers.
Be sure to check out the Illinois State Archives. There are many links to information about doing genealogical research in Illinois, the Illinois Regional Archives Depository System (IRAD), and online databases. Their holdings include digitals of the Federal Township Plats of Illinois.
There are many databases to check at the Illinois State Archives. These include Illinois Statewide Marriage Index, 1763-1900, Illinois Statewide Death Index, Pre-1916 and Illinois Statewide Death Index 1916-1950. There is a listing of records in IRAD, plus lists of veterans. I particularly like the Illinois Civil War Muster and Descriptive Rolls Database.
If you have Chicago ancestors, be sure to check out the Chicago Public Library Digital Collections. Another interesting web page is Chicago Ancestors.org from The Newberry Library.
There's more out there, so be sure to Google for your areas of interest in Illinois and include the word "digital."